[NET]: Size listen hash tables using backlog hint

We currently allocate a fixed size (TCP_SYNQ_HSIZE=512) slots hash table for
each LISTEN socket, regardless of various parameters (listen backlog for
example)

On x86_64, this means order-1 allocations (might fail), even for 'small'
sockets, expecting few connections. On the contrary, a huge server wanting a
backlog of 50000 is slowed down a bit because of this fixed limit.

This patch makes the sizing of listen hash table a dynamic parameter,
depending of :
- net.core.somaxconn tunable (default is 128)
- net.ipv4.tcp_max_syn_backlog tunable (default : 256, 1024 or 128)
- backlog value given by user application  (2nd parameter of listen())

For large allocations (bigger than PAGE_SIZE), we use vmalloc() instead of
kmalloc().

We still limit memory allocation with the two existing tunables (somaxconn &
tcp_max_syn_backlog). So for standard setups, this patch actually reduce RAM
usage.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 10 deletions

diff --git a/net/core/request_sock.c b/net/core/request_sock.c
index 79ebd75fbe4d..5f0818d815e6 100644
--- a/net/core/request_sock.c
+++ b/net/core/request_sock.c
@@ -15,6 +15,7 @@
 #include <linux/random.h>
 #include <linux/slab.h>
 #include <linux/string.h>
+#include <linux/vmalloc.h>
 
 #include <net/request_sock.h>
 
@@ -29,22 +30,31 @@
  * it is absolutely not enough even at 100conn/sec. 256 cures most
  * of problems. This value is adjusted to 128 for very small machines
  * (<=32Mb of memory) and to 1024 on normal or better ones (>=256Mb).
- * Further increasing requires to change hash table size.
+ * Note : Dont forget somaxconn that may limit backlog too.
  */
 int sysctl_max_syn_backlog = 256;
 
 int reqsk_queue_alloc(struct request_sock_queue *queue,
-                      const int nr_table_entries)
+                      unsigned int nr_table_entries)
 {
-        const int lopt_size = sizeof(struct listen_sock) +
-                              nr_table_entries * sizeof(struct request_sock *);
-        struct listen_sock *lopt = kzalloc(lopt_size, GFP_KERNEL);
-
+        size_t lopt_size = sizeof(struct listen_sock);
+        struct listen_sock *lopt;
+
+        nr_table_entries = min_t(u32, nr_table_entries, sysctl_max_syn_backlog);
+        nr_table_entries = max_t(u32, nr_table_entries, 8);
+        nr_table_entries = roundup_pow_of_two(nr_table_entries + 1);
+        lopt_size += nr_table_entries * sizeof(struct request_sock *);
+        if (lopt_size > PAGE_SIZE)
+                lopt = __vmalloc(lopt_size,
+                        GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
+                        PAGE_KERNEL);
+        else
+                lopt = kzalloc(lopt_size, GFP_KERNEL);
         if (lopt == NULL)
                 return -ENOMEM;
 
-        for (lopt->max_qlen_log = 6;
-             (1 << lopt->max_qlen_log) < sysctl_max_syn_backlog;
+        for (lopt->max_qlen_log = 3;
+             (1 << lopt->max_qlen_log) < nr_table_entries;
              lopt->max_qlen_log++);
 
         get_random_bytes(&lopt->hash_rnd, sizeof(lopt->hash_rnd));
@@ -65,9 +75,11 @@ void reqsk_queue_destroy(struct request_sock_queue *queue)
 {
         /* make all the listen_opt local to us */
         struct listen_sock *lopt = reqsk_queue_yank_listen_sk(queue);
+        size_t lopt_size = sizeof(struct listen_sock) +
+                lopt->nr_table_entries * sizeof(struct request_sock *);
 
         if (lopt->qlen != 0) {
-                int i;
+                unsigned int i;
 
                 for (i = 0; i < lopt->nr_table_entries; i++) {
                         struct request_sock *req;
@@ -81,7 +93,10 @@ void reqsk_queue_destroy(struct request_sock_queue *queue)
         }
 
         BUG_TRAP(lopt->qlen == 0);
-        kfree(lopt);
+        if (lopt_size > PAGE_SIZE)
+                vfree(lopt);
+        else
+                kfree(lopt);
 }
 
 EXPORT_SYMBOL(reqsk_queue_destroy);